Uplink power control in aggregated spectrum systems

ABSTRACT

A method for communication includes modulating data in a wireless communication terminal to produce an aggregated-spectrum signal, which includes at least first and second signals in respective first and second spectral bands. The modulated data is transmitted in the first and second signals at respective first and second power levels. The second power level is adjusted separately from the first power level. In some embodiments, one or more instructions to set the first power level are received at the wireless communication terminal, and the first power level is set separately from setting the second power level based on the instructions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/348,375, filed Jan. 5, 2009, which claims the benefit of U.S.Provisional Patent Application 61/081,130, filed Jul. 16, 2008, and U.S.Provisional Patent Application 61/115,714, filed Nov. 18, 2008. Thedisclosures of all these related applications are incorporated herein byreference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication systems, andparticularly to methods and systems for power control in wirelesscommunication systems.

BACKGROUND

Various communication systems modify the power of transmitted signals inorder to adapt to current channel conditions. Such techniques arecommonly referred to as power control. For example, 3^(rd) GenerationPartnership Project (3GPP) Evolved Universal Terrestrial Radio Access(E-UTRA) systems apply power control to the uplink signals. The uplinkpower control methods applied in E-UTRA systems are specified, forexample, in 3GPP Technical Specification 36.213, entitled “TechnicalSpecification Group Radio Access Network; Evolved Universal TerrestrialRadio Access (E-UTRA); Physical Layer Procedures (Release 8),” (3GPP TS36.213), version 8.4.0., September, 2008, which is incorporated hereinby reference.

E-UTRA is also commonly known as Long-Term Evolution (LTE). An advancedversion of E-UTRA, which is commonly known as LTE-Advanced (LTE-A), iscurrently being specified by the 3GPP standardization bodies. In thecontext of the present patent application and in the claims, the term“E-UTRA specification” refers to any E-UTRA, LTE or LTE-A specification,as well as to subsequent versions of these specifications.

Uplink power control is useful, for example, for reducing interferenceand increasing spectral efficiency in cellular communication networks.Some aspects of interference mitigation and spectral efficiencyimprovement are addressed in a report published by the 3GPP TechnicalSpecification Group Radio Access Network Working Group 1 (TSG-RAN WG1),entitled “Interference Mitigation via Power Control and FDM ResourceAllocation and UE Alignment for E-UTRA Uplink and TP,” (R1-060401),Denver, Colo., Feb. 13-17, 2006, which is incorporated herein byreference. Uplink power control in E-UTRA systems is also discussed inTSG-RAN WG1 report R1-070795, entitled “Uplink Power Control forE-UTRA,” Saint-Louis, Mo., Feb. 12-16, 2007, which is incorporatedherein by reference.

Some LTE-A systems deploy carrier aggregation techniques, in which awireless terminal communicates with a base station over multipleaggregated LTE or LTE-A carriers to provide high bandwidth capabilities.Carrier aggregation (also referred to as spectrum aggregation) isdescribed, for example, in TSG-RAN WG1 report R1-082468, entitled“Carrier Aggregation in LTE-Advanced,” Warsaw, Poland, Jun. 30-Jul. 4,2008, which is incorporated herein by reference.

SUMMARY

An embodiment that is described herein provides a method forcommunication:

In a wireless communication terminal, data is modulated to produce anaggregated-spectrum signal including at least first and second signalsin respective first and second spectral bands. The modulated data istransmitted in the first and second signals at respective first andsecond power levels.

The second power level is adjusted separately from the first powerlevel.

Another embodiment that is described herein provides a method forcommunication:

In a wireless communication terminal, data is modulated to produce anaggregated-spectrum signal including at least first and second signalsin respective first and second spectral bands. The modulated data istransmitted in the first and second spectral bands at respective firstand second power levels.

One or more instructions to set the first power level are received atthe wireless communication terminal.

The first power level is set separately from setting the second powerlevel, wherein the first power level is set based on the instructions.

In an embodiment, each of the signals conforms to an Evolved UniversalTerrestrial Radio Access (E-UTRA) specification. In a disclosedembodiment, the method includes receiving at the wireless communicationterminal one or more additional instructions to set the second powerlevel, and setting the second power level based on the additionalinstructions. In an embodiment, receiving the one or more additionalinstructions includes receiving the additional instructions to setrespective power levels of additional signals other than the first andsecond signals, and setting the power levels of the first and secondsignals and of the additional signals separately based on theinstructions and the additional instructions. In some embodiments, thesignals are divided into two or more subsets, and receiving theinstructions includes receiving a single power level setting for thesignals includes in each of the subsets. In an embodiment, transmittingthe modulated data includes transmitting the modulated data in the firstand second non-contiguous spectral bands.

Yet another embodiment that is described herein provides a wirelesscommunication terminal, including a transmitter, a receiver and aprocessor.

The transmitter modulates data to produce an aggregated-spectrum signalincluding at least first and second signals in respective first andsecond spectral bands, and transmits the modulated data in the first andsecond signals at respective first and second power levels.

The receiver receives one or more instructions to set the first powerlevel.

The processor sets the first power level separately from setting thesecond power level, wherein the first power level is set based on theinstructions.

Another disclosed embodiment provides a wireless communication terminal,including a transmitter and a processor.

The transmitter modulates data to produce an aggregated-spectrum signalincluding at least first and second signals in respective first andsecond spectral bands and transmits the modulated data in the first andsecond signals at respective first and second power levels.

The processor adjusts the second power level separately from the firstpower level.

An additional embodiment that is described herein provides a method forcommunication:

In a wireless communication terminal, data is modulated to produce anaggregated-spectrum signal including at least first and second signalsin respective first and second spectral bands, each of which includes aplurality of sub-carriers. The modulated data is transmitted in thefirst and second signals at respective first and second power levels.

Downlink signals, which govern a first transmission parameter of themodulated data transmitted on the sub-carriers in the first signal, arereceived and processed separately from a second transmission parameterof the modulated data transmitted on the sub-carriers in the secondsignal.

Yet another embodiment that is described herein provides a mobilecommunication terminal, including a transmitter and a power controlmodule.

The transmitter transmits modulated data over at least first and secondsignal carriers in an aggregated spectrum during a time interval.

The power control module controls a power characteristic of themodulated data transmitted on the first signal carrier separately fromthe power characteristic of the modulated data transmitted on the secondsignal carrier.

Another embodiment that is described herein provides a base station,including a receiver, a transmitter and a processor.

The receiver receives from a wireless communication terminal at leastfirst and second carriers, over which data has been modulated and whichhave been transmitted during a communication time interval at respectivefirst and second power levels.

The processor produces one or more instructions to set the first powerlevel separately from setting the second power level.

The transmitter transmits the one or more instructions to the wirelesscommunication terminal.

An additional embodiment that is described herein provides acommunication system.

The communication systems includes a base station and a wirelesscommunication terminal.

The wireless communication terminal includes a transmitter, a receiverand a processor.

The transmitter modulates data to produce an aggregated-spectrum signalincluding at least first and second signals in respective first andsecond spectral bands, and transmits the modulated data in the first andsecond signals at respective first and second power levels to a basestation.

The receiver receives from the base station one or more instructions toset the first power level.

The processor sets the first power level separately from setting thesecond power level, wherein the first power level is set based on theinstructions.

Yet another embodiment that is described herein provides a communicationsystem.

The communication system includes a base station and a wirelesscommunication terminal.

The wireless communication terminal includes a transmitter and aprocessor.

The transmitter modulates data to produce an aggregated-spectrum signalincluding at least first and second signals in respective first andsecond spectral bands, and transmits the modulated data in the first andsecond signals at respective first and second power levels to the basestation.

The processor adjusts the second power level separately from the firstpower level.

An additional embodiment that is described herein provides a method forcommunication.

In a wireless communication terminal, data is modulated to produce anaggregated-spectrum signal including at least first and second signalsin respective first and second spectral bands. The modulated data istransmitted in the first and second spectral bands at respective firstand second power levels.

Downlink signals are received at the wireless communication terminal.

The first power level is set based on the second power level and onmeasurements performed on the downlink signals.

Yet another embodiment that is described herein provides a wirelesscommunication terminal, including a transmitter, a receiver and aprocessor.

The transmitter modulates data to produce an aggregated-spectrum signalincluding at least first and second signals in respective first andsecond spectral bands, and transmits the modulated data in the first andsecond signals at respective first and second power levels.

The receiver receives downlink signals.

The processor performs measurements on the downlink signals and sets thefirst power level based on the second power level and on themeasurements.

The present disclosure will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that schematically illustrates a wirelesscommunication system that employs spectrum aggregation, in accordancewith an embodiment that is described herein;

FIG. 2 is a flow chart that schematically illustrates a method foruplink power control in a spectrum aggregation system, in accordancewith an embodiment that is described herein;

FIG. 3 is a block diagram that schematically illustrates a wirelessterminal that employs spectrum aggregation with uplink power control, inaccordance with an embodiment that is described herein; and

FIGS. 4-6 are block diagrams that schematically illustrate wirelessterminal transmitter chain configurations, in accordance withembodiments that are described herein.

DETAILED DESCRIPTION OF EMBODIMENTS

In a typical wireless spectrum aggregation system, data is transmittedover two or more spectral bands. A Radio Frequency (RF) carrier signalis associated with each of these spectral bands, and data is modulatedover each carrier. The two or more spectral bands may be contiguous ornon-contiguous. For example, in LTE-A spectrum aggregation, each carrierconforms to the E-UTRA specification, cited above. As noted above,accurate uplink power control is important for maintaining optimumsystem performance. When using spectrum aggregation, each uplink carriermay experience different channel conditions (e.g., different path lossand/or interference), even though the different carriers are transmittedbetween the same two endpoints. Therefore, the optimum transmit powerlevel may differ from one uplink carrier to another.

Embodiments that are described hereinbelow provide methods and systemsfor uplink power control in spectrum aggregation systems. The methodsand systems described herein control the power levels of the differentuplink carriers, so as to match the specific conditions of each carrier.As a result, system performance, such as capacity, spectral efficiencyand interference mitigation, are not compromised by carrier-to-carriervariations.

In some embodiments, the wireless terminal calculates and sets thetransmit power level of each uplink carrier in response to instructionsreceived from a base station. The base station may comprise a cellularbase station or any other suitable access point connected to a network.The instructions may comprise, for example, incremental closed-loopinstructions to increase or decrease the power level of a given carrier,based on measurements performed by the base station on the receiveduplink signal. Additionally or alternatively, the terminal may measurethe downlink signal received from the base station, estimate thedownlink path loss and set the power level of a given uplink carrierbased on the estimated downlink path loss. In this embodiment, theinstructions provided by the base station may comprise corrections thatare to be applied in open-loop to the estimated path loss.

In some embodiments, the base station sends closed-loop instructionsand/or open-loop corrections individually for each uplink carrier. Inalternative embodiments, the carriers are divided into groups, and thebase station sends instructions per carrier group. This feature reducesthe amount of signaling information that is transmitted over thedownlink. Generally, the terminal and the base station may operateopen-loop and/or closed-loop processes per each individual carrier, pereach carrier group and/or jointly for all carriers. Several examples ofwireless terminal configurations, which carry out uplink power controlof aggregated carriers, are described herein.

FIG. 1 is a block diagram that schematically illustrates a wirelesscommunication system 20 that employs spectrum aggregation, in accordancewith an embodiment that is described herein. System 20 comprises awireless communication terminal 24, which communicates with a BaseStation 28 over a wireless channel. In the present example, system 20comprises an Long Term Evolution Advanced (LTE-A) system, in whichterminal 24 is referred to as a User Equipment (UE) and BS 28 isreferred to as an enhanced Node-B (eNodeB). In alternative embodiments,however, system 20 may conform to any other suitable communicationstandard or specification. For example, system 20 may comprise a WiFisystem operating in accordance with the IEEE 802.11 specification, aWiMAX system operating in accordance with the IEEE 802.16 specification,or a Mobile Broadband Wireless Access (MBWA) system operating inaccordance with the IEEE 802.20 specification. The example of FIG. 1refers to only a single UE and a single BS for the sake of clarity,although real-life systems typically comprise multiple UEs and multipleBSs.

In accordance with an embodiment, system 20 employs spectrumaggregation, meaning that UE 24 and BS 28 may communicate over multiplecarriers simultaneously. When using spectrum aggregation, UE 24transmits to the BS an uplink signal, which comprises two or moreaggregated spectral bands. Each spectral band is referred to herein as acarrier or a component carrier. Each such carrier may comprise multiplesub-carriers, such as in LTE systems in which each carrier comprisesmultiple Orthogonal Frequency Division Multiplexing (OFDM) sub-carriers.Note that in some embodiments (e.g., OFDM), transmission within eachcarrier is performed in designated time/frequency bins. In some cases,the time bins allocated in different carriers do not necessarilyoverlap, even though the carriers are transmitted simultaneously. Theterm “simultaneously” should be understood as referring to suchscenarios, as well.

UE 24 may transmit any number of aggregated carriers. The carriers maybe transmitted in adjacent or non-contiguous spectral bands. Typically,each carrier has a bandwidth in the range of 1.4-20 MHz, although othersuitable bandwidths can also be used. Communication over multipleaggregated carriers provides high bandwidth, e.g., up to 100 MHz. Thedescription that follows focuses on spectrum aggregation in the uplinkchannel (i.e., from the UE to the BS). Typically, however, spectrumaggregation is applied in both uplink and downlink channels.

UE 24 comprises a modulator/demodulator (modem) 32, which modulates datato be transmitted over the uplink channel. The modulated data isprovided to a UE Radio Frequency Front End (RF FE) 36, which typicallyconverts the digital modem output to an analog signal using a suitableDigital to Analog Converter (DAC), up-converts the analog signal to RFand amplifies the RF signal to the appropriate transmission power. TheRF FE may also perform functions such as filtering, as is known in theart. The RF signal at the output of RF FE 36 is transmitted via a BSantenna 40 toward UE BS 28.

UE 24 further comprises a UE controller 44, which configures andcontrols the different elements of the UE. In particular, controller 44comprises a Power Control (PC) unit 48, which computes and sets thetransmission power of each carrier transmitted by the UE, using methodsthat will be explained in greater detail below.

The RF signal transmitted from the UE is received at the BS by a BSantenna 52, and is provided to a BS RF FE 56. RF FE 56 down-converts thereceived RF signal to a suitable low frequency (e.g., to baseband), anddigitizes the signal using a suitable Analog to Digital Converter (ADC).The digitized signal is provided to a BS modem 60, which demodulates thesignal and attempts to reconstruct the data that was provided to modem32 at the UE. BS 28 further comprises a BS processor 64, whichconfigures and controls the different elements of the BS. In particular,processor 64 comprises a PC unit 68, which sends PC-related instructionsto the UE, as will be explained further below.

The description above refers to uplink transmission, i.e., transmissionfrom the UE to the BS. On downlink transmission, the different elementsof the UE and BS typically perform the opposite functions. In otherwords, BS modem 60 modulates the uplink signal. RF FE 56 up-converts thesignal to RF and transmits the signal toward the UE via antenna 52. Thedownlink RF signal is received by UE antenna 40, down-converted by RF FE36 and demodulated by UE modem 32. The configuration of UE 24 and BS 28shown in FIG. 1 is a simplified example configuration, which was chosenfor the sake of conceptual clarity. In alternative embodiments, anyother suitable UE and BS configurations can be used. Several examples ofthe internal structure and functionality of UE 24 are shown in FIGS. 3-6below.

Typically, UE controller 44 and BS processor 64 comprise general-purposeprocessors, which are programmed in software to carry out the functionsdescribed herein. The software may be downloaded to the processors inelectronic form, over a network, for example, or it may, alternativelyor additionally, be provided and/or stored on tangible media, such asmagnetic, optical, or electronic memory. Additionally or alternatively,elements of controller 44 and processor 64 may be implemented inhardware or firmware, such as using Application-Specific IntegratedCircuits (ASICs) or other hardware components.

In the example of FIG. 1, UE 24 transmits an aggregated signal, whichcomprises three LTE-compliant carriers 72A . . . 72C. Generally, the UEmay allocate bandwidth over any of the carriers to transmission of dataitems in any desired manner. In the present example, a data item 76A istransmitted over carrier 72A and some of the bandwidth (i.e., some ofthe sub-carriers) of carrier 72B. Another data item 76B is transmittedover some of the bandwidth of carrier 72B, as well as over carrier 72C.

The multiple uplink carriers transmitted by UE 24 are all transmittedbetween the same two endpoints. Nevertheless, in many practical cases,different carriers in the aggregated signal experience different channelconditions. For example, the path loss between the UE and the BS maydiffer from one carrier to another, such as because of differentpropagation or multipath effects that vary over frequency. Thedifference in path loss is particularly noticeable when the carriersoccupy non-contiguous, widely-spaced frequency bands. As anotherexample, different carriers may suffer from different levels ofinterference (e.g., interference from other UEs, which may communicatewith the same BS or with other BSs). As yet another example, differentcarriers may have different transmission characteristics (e.g.,different modulation or error correction coding).

As noted above, accurate setting of the carrier transmission power levelis important for optimizing the performance of system 20. Sincedifferent carriers in the aggregated signal may experience differentconditions, the optimal transmit power level may also differ from onecarrier to another. Embodiments that are described herein providemethods and systems for performing uplink power control in spectrumaggregation systems. The methods and systems described herein computeand set the transmit power level individually per carrier, so that theUE transmits each carrier at a power level that matches its specificconditions. As can be seen in the example of FIG. 1, carriers 72A . . .C have different power levels, which are determined and set to match thespecific conditions of each carrier.

In the example embodiment of FIG. 1, each carrier conforms to the E-UTRAspecification. Each carrier comprises multiple sub-carriers that aremodulated using OFDM. In such embodiments, the power control methodsdescribed herein preserve the relative power ratios among the individualsub-carriers within a given carrier.

In some embodiments, the power level of a given uplink carrier may bedetermined using an open-loop process and a closed-loop process, whichoperate concurrently with one another. In the open-loop process, the UEmeasures the downlink signal received from the BS and estimates the pathloss for the carrier in question. Assuming that the downlink path lossis indicative of the uplink path loss, the UE uses the estimated pathloss to set the appropriate transmit power level of the uplink carrier.

Typically, the UE periodically corrects the uplink carrier power level(which was computed based on the estimated downlink path loss) by acorrection factor that is provided by the BS. The correction factor istypically signaled to the UE using higher link layers, e.g., using RadioResource Control (RRC) signaling. The correction factor may servevarious purposes. For example, the BS may apply a policy in which UEs atthe edge of the cell transmit at a lower power level in order to reduceinterference to neighboring cells. In order to enforce such a policy,the BS may send to the UE a correction factor, which depends on thedistance between the UE and the BS. Additionally or alternatively, thecorrection factor may account for errors and inaccuracies of the pathloss estimation performed by the UE.

In the closed-loop process, the BS sends to the UE instructions toincrease or decrease the power level on a given uplink carrier, based onmeasurements performed by the BS on the received uplink signal. The UEdecodes these instructions (sometimes referred to as Transmit PowerControl—TPC) and adjusts the power level of the given carrieraccordingly. The closed-loop instructions are typically incremental,i.e., request the UE to increase or decrease the carrier power level bya certain increment, e.g., 1 dB.

The open-loop and closed-loop processes typically operate concurrentlywith one another, but at different time constants. The open-loopcorrections (i.e., the corrections that are to be applied to the uplinkpower levels based on the estimated downlink path loss) are typicallyapplied by the UE only occasionally, at relatively large time intervals(e.g., on the order of seconds, although other time constants can alsobe used). The closed-loop process, on the other hand, provides TPCinstructions at a relatively high rate in comparison with the open-loopcorrections. Note that is some cases only the closed-loop process isactive and the open-loop process is inhibited. In other cases, theopen-loop process may be given varying weights. For example, in theabove-cited LTE specification, a parameter denoted α controls the weightgiven to the open-loop process (α=1 means that both open-loop process isactive and receives full weight, α=0 means that only the closed-loop isactive).

For example, in some implementations each cell has a constant set ofopen-loop correction factors, which are updated when the UE hands-off toa different cell but remain constant otherwise. The UE may estimate thedownlink path at any desired rate, such as every few seconds. These timeintervals may change, for example as a function of the distance betweenthe UE and the BS. In a typical implementation, the update rate of theclosed loop is usually in the range of 20 Hz to 1 kHz, with a typicalrate of 100 Hz, although any other suitable update rate can also beused. The exact rate depends on the Node-B strategy The UE sets thetransmit power level of each uplink carrier using both processes, i.e.,based on both the open-loop correction factor provided by the BS and onthe closed-loop TPC instructions.

In some embodiments, the BS and UE may operate an open-loop process anda closed-loop process for each carrier, independently of open- andclosed-loop processes of other carriers. In these embodiments, the BSsends open-loop correction factors and closed-loop instructionsseparately for each carrier. The UE receives and processes the open-loopcorrection factors and closed-loop instructions and adjusts the powerlevels of the different carriers accordingly.

In alternative embodiments, the BS and UE operate a common closed-loopprocess for all the uplink carriers, and separate open-loop processesper carrier. In these embodiments, the BS transmits closed-loopinstructions that apply to all carriers that are aggregated by the UE.In addition, the BS transmits a separate open-loop correction factor foreach carrier. The UE sets the transmit power level of a given carrierbased on the correction factor corresponding to this carrier and on thecommon closed-loop instructions. Sending common closed-loop instructionsto multiple carriers reduces the amount of signaling information that issent over the downlink, especially since the closed-loop instructionsare sent at relatively frequent intervals.

In some embodiments, the amount of signaling information sent over thedownlink is reduced by dividing the uplink carriers into groups. Inthese embodiments, the uplink carriers transmitted by the UE are dividedinto two or more groups, and the BS and UE operate a common closed-loopprocess for each group. In these embodiments, the BS transmitsclosed-loop instructions applying to all the carriers in a given group,without duplicating the instructions for each carrier in the group. TheUE receives the closed-loop instructions and calculates the power levelof a given uplink carrier based on the closed-loop instructionscorresponding to the group to which the carrier belongs.

The number of groups, the number of carriers in each group and themapping of carriers to groups can be selected in any desired manner. Forexample, it may be advantageous to map carriers that occupy nearbyfrequencies to the same group, since the channel conditions experiencedby these carriers are more likely to be similar. Consequently, applyingthe same closed-loop instructions to such a group of carriers is morelikely to be accurate.

When the closed-loop process is common to two or more carriers, the BSmay send to the UE power offsets to be applied to these differentcarriers. In these embodiments, the UE sets the power level of a givencarrier based on the common closed-loop instructions, but applies acarrier-specific power offset to each carrier. Typically, the poweroffsets are signaled to the UE via higher layers (e.g., using RRCsignaling), similarly to the open-loop correction factors.

In some embodiments, the UE determines the power level of a given uplinkcarrier based on (1) the power level of another uplink carriertransmitted by the UE, and (2) downlink signal measurements performed bythe UE. This sort of technique is useful, for example, when the UE addsa new uplink carrier to the spectrum-aggregated signal, which alreadycomprises one or more existing carriers. In such a scenario, the UE doesnot yet have closed-loop information from the BS, since the new carrierwas not yet measured by the BS. The power levels of the existingcarriers, on the other hand, are typically already set to the desiredvalues. Therefore, the UE may set the initial power level of the newcarrier relatively to the power levels of the existing carriers. In someembodiments, the UE corrects this initial power level based oninter-carrier power offsets that can be estimated from open-loopmeasurements on the downlink signals.

The above-mentioned embodiments are described by way of example. Theseembodiments focus mainly on reducing the number of closed-loopinstructions sent over the downlink, since these instructions arerelatively frequent and consume more downlink resources in comparisonwith open-loop correction factors. In alternative embodiments, however,the BS and UE may operate closed-loop and/or open-loop processes for anydesirable carrier or group of carriers. For example, the power level ofsome carriers may be set using only open-loop or using only closed-loopprocessing. As another example, the BS may transmit common open-loopcorrections that apply to two or more carriers.

The selection of an appropriate power control loop configuration maydepend on various system considerations. For example, in some systemconfigurations the carrier aggregation may be different in the uplinkand in the downlink. In these system configurations, the downlink pathloss may not accurately indicate the uplink path loss, and therefore theopen-loop process may produce relatively large errors. In theseconfigurations it may be preferable to operate a separate closed-loopprocess for each uplink carrier in order to compensate for these errors.

The open-loop process may also produce relatively large errors insystems in which the uplink and downlink are multiplexed using FrequencyDivision Duplex (FDD), since the uplink and downlink frequencies aredifferent. A dedicated closed-loop process per uplink carrier may bepreferable in these configurations, as well. In system configurationsthat multiplex the uplink and downlink using Time Division Duplex (TDD),operating a closed-loop process per a group of carriers (or even for allcarriers) may be sufficient. As noted above, this choice may also dependon the frequency separation between uplink carriers.

FIG. 2 is a flow chart that schematically illustrates a method foruplink power control in spectrum aggregation system 20, in accordancewith an embodiment that is described herein. Operations 80-88 belowillustrate the open-loop process, and operations 92-96 below illustratethe closed-loop process. Typically, the two processes are carried outconcurrently. (As noted above, the open-loop process may sometimes beinhibited, in which case operations 80-88 below are omitted.) Theopen-loop process begins with UE 24 receiving open-loop correctionfactors from BS 28, at an open-loop reception operation 80. Eachopen-loop correction may apply to a single uplink carrier or to a groupof carriers. Additionally or alternatively, in embodiments in which aclosed-loop process is operated jointly for two or more carriers, the UEmay receive from the BS power offsets to be applied to each of thesecarriers. The open-loop correction factors and/or power offsets aretypically provided to the UE using higher layer signaling, such as RRCsignaling.

The UE measures the downlink signal received from the BS and estimatesthe downlink path loss, at a path loss estimation operation 84. The UEmay estimate the downlink path loss by measuring the downlink signalstrength (sometimes referred to as Received Signal StrengthIndication—RSSI). Additionally or alternatively, the UE may measure thesignal strength only over pilot symbols transmitted in the downlinksignal. This measure is sometimes referred to as Reference SignalReceived Power—RSRP). Further additionally or alternatively, the UE mayperform any other suitable measurements for assessing the downlink pathloss. The path loss may be estimated per each carrier or group ofcarriers. The UE applies the open-loop correction factors to thecorresponding measured path losses, at an open-loop factoring operation88. The result of operation 88 is a set of one or more path losses, onefor each carrier or group of carriers, which are adjusted based on afactor specified by the BS.

The closed-loop process begins with the UE receiving from the BSclosed-loop TPC instructions, at a closed-loop reception operation 92.The closed-loop instructions request the UE to increase or decrease thepower level on a given uplink carrier or group of carriers, based onmeasurements performs by the BS on the received uplink signal, asexplained above. The UE decodes the closed-loop instructions andcomputes the appropriate correction to be applied to each uplinkcarrier, at a closed-loop computation operation 96.

At this point, the UE possesses both open-loop corrections andclosed-loop instructions, which are to be applied to each uplinkcarrier. Based on these parameters, the UE calculates the power level ofeach uplink carrier, at a power level computation operation 100. The UEconfigures its transmitter to transmit each carrier at the computedpower level.

In some embodiments, the UE sets the power level of a given PhysicalUplink Shared Channel (PUSCH) in a given LTE subframe on a given uplinkcarrier, which is associated with a given carrier group, according tothe following formula:

P _(PUSCH)(i,c)=min{P _(MAX),10 log₁₀(M _(PUSCH)(i))+P _(O) _(—)_(PUSCH)(c)+α(c)·PL(c)+Δ_(TF)(i,c)+f(i,g)}  Equation 1

The above formula uses a notation similar to the notation used insection 5.1.1.1 of the 3GPP TS 36.213 v8.4.0 specification, cited above.P_(PUSCH)(i,c) is expressed in dBm. i denotes a subframe index, cdenotes an index of the uplink carrier, and g denotes an index of thecarrier group for which a closed-loop process is operated jointly.P_(MAX) denotes the maximum power allowed to the power class to whichthe UE belongs. M_(PUSCH)(i) denotes the bandwidth of the PUSCH resourceassignment, expressed as a number of resource blocks that are valid forsubframe i. P_(O) _(—) _(PUSCH)(c) denotes a parameter composed of thesum of a cell-specific nominal component P_(O) _(—) _(NOMINAL) _(—)_(PUSCH), which is signaled from higher UE layers, and a UE-specificcomponent P_(O) _(—) _(UE) _(—) _(PUSCH)(c) for the c-th carrier, whichis configured by RRC signaling.

α(c)ε{0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1} denotes a cell-specificparameter for the c-th carrier, which is provided by the higher layers.PL(c) denotes the downlink path loss estimate of the c-th carrier, asestimated by the UE. Δ_(TF)(i,c)=10 log₁₀(2^(MPR(i)·K) ^(S) ^((c))−1),wherein K_(S)(c) denotes a cell-specific parameter for the c-th carriergiven by RRC. MPR(i) is a parameter defined in the 3GPP TS 36.213specification. Let δ_(PUSCH) denote the transmit power correction valueper group of carriers, which is provided to the UE in the closed-loopTPC instructions.

If the UE-specific parameter Accumulation-enabled, which is provided byhigher layers as defined in the 3GPP TS 36.213 specification, indicatesthat accumulation is enabled, the current PUSCH power control adjustmentstate for the g-th group is given byf(i,g)=f(i−1,g)+δ_(PUSCH)(i−K_(PUSCH),g), wherein f (0,g)=0,δ_(PUSCH)(i−K_(PUSCH),g) was signaled on subframe i−K_(PUSCH), andK_(PUSCH) is defined in the 3GPP TS 36.213 specification.

Otherwise, i.e., if accumulation is not enabled, the current PUSCH powercontrol adjustment state for the g-th group is given byf(i,g)=δ_(PUSCH)(i−K_(PUSCH),g) wherein δ_(PUSCH)(i−K_(PUSCH),g) wassignaled on subframe i−K_(PUSCH).

Alternatively, the UE can calculate the transmit power of a givencarrier using any other suitable method or formula. The UE transmits theuplink signal, at an uplink transmission operation 104. The uplinksignal comprises multiple aggregated LTE-A carriers, with each carriertransmitted at the power level determined at operation 100 above. Sincethe UE and BS operate individual open- and/or closed-loop processes foreach carrier or group of carriers, the power level of any given uplinkcarrier matches the specific conditions seen by this carrier. As aresult, highly accurate uplink power control can be achieved.

FIG. 3 is a block diagram that schematically illustrates an example ofan internal structure of UE 24, in accordance with an embodiment that isdescribed herein. In the example of FIG. 3, the UE comprises atransmitter 110 and a receiver 114, which interact with higher UE layers118, as well as with RF FE 36.

Receiver 114 comprises a receive (RX) path 122, which accepts a receivedand down-converted downlink signal from RF FE 36. The RX path (typicallyimplemented as part of modem 32 of FIG. 1 above) demodulates the signaland provides the data and control information conveyed by the signal tothe higher UE layers.

The receiver further comprises a signal measurement unit 126, whichmeasures the downlink signal strength. Unit 126 can measure, forexample, the RSSI or RSRP of the downlink signal, or any other suitablesignal measure. The signal measurement results are provided to a pathloss estimation unit 130, which computes an estimate of the downlinkpath loss and provides path loss estimates to transmitter 110. Receiver114 further comprises a TPC decoder 134, which decodes the closed-loopTPC instructions received from the BS. Decoder 134 provides theclosed-loop power corrections conveyed in these instructions totransmitter 110. As noted above, any of the TPC instructions, downlinksignal strength measurements and/or path loss estimates may applyjointly to all uplink carriers, to an individual carrier or to aspecified group of carriers.

Transmitter 110 comprises a transmit (TX) path 142, which accepts dataand control information for transmission from the higher UE layers,modulates the data over multiple aggregated LTE-A carriers and providesthe spectrum-aggregated signal to RF FE 36. The TX path is typicallyimplemented as part of modem 32 of FIG. 1.

Transmitter 110 further comprises a Power Control (PC) unit 138, similarin functionality to unit in FIG. 1 above. The PC unit receives downlinkpath loss estimates from path loss estimation unit 130 and closed-looppower corrections from decoder 134. In addition, PC unit 138 acceptsopen-loop corrections from a PC setup function in the higher UE layers.Based on the various open-loop and closed-loop parameters, PC unit 138computes the desired power level of each uplink carrier using themethods described above.

The PC unit typically controls TX path 142 and/or RF FE 36, so as tocause the UE to transmit each uplink carrier at its designated powerlevel. The PC unit can configure the power level of a given carrier bysetting the digital gain of the TX path and/or the analog gain of the RFFE for transmitting this carrier. In some embodiments, the TX path hasat least one configurable digital gain stage, and the PC unit controlsthe digital gain of the TX path to set the desired carrier power level.Additionally or alternatively, the RF FE may comprise at least oneconfigurable analog gain stage, whose analog gain is controlled by thePC unit. Several example transmitter configurations having configurabledigital and analog gain stages are described in FIGS. 4-6 below.

The configuration of UE 24 seen in FIG. 3 is an example configuration,which is chosen for the sake of conceptual clarity. In otherembodiments, any other suitable UE configuration can also be used. Thedifferent elements shown in FIG. 3 can be implemented in suitablededicated hardware, in software running on general-purpose hardware, orusing a combination of hardware and software elements.

FIG. 4 is a block diagram that schematically illustrates an uplinktransmitter chain 150 in UE 24, in accordance with an embodiment that isdescribed herein. Referring to FIG. 3 above, the transmitter chaincomprises elements belonging to TX path 142, as well as elementsbelonging to RF FE 36. Transmitter chain 150 comprises a digitaltransmitter (modulator) 154, which produces a baseband digital signal.The output of transmitter 154 (denoted TxData) is amplified by aconfigurable digital gain stage 158. The digital gain of stage 158 isset by PC unit 138 of FIG. 3.

The output of digital gain stage 158 is converted to an analog signal bya Digital-to-Analog (D/A) converter 162. In the present example, D/A 162comprises a pair of converters, which produce an In-phase/Quadrature(I/Q) signal. The I/Q signal is processed by an analog unit 166, whichtypically comprises one or more filters and one or more amplifiers. Unit166 has a configurable analog gain, which is set by PC unit 138. Theoutput of unit 166 is up-converted by a mixer 170 to the desired RadioFrequency (RF). The mixer up-converts the signal by mixing it with asuitable Local Oscillator (LO) signal. The RF signal is then amplifiedby a Power Amplifier (PA) 174. The PA output is fed to UE antenna 40.

In some embodiments, the UE may comprise multiple transmitter chains150, and each uplink carrier is transmitted by a separate transmitterchain. The power level at which the carrier is transmitted depends onthe values of the digital gain and the analog gain that are set by PCunit 138. A given power level can be reached using various combinationsof digital and analog gain values. However, some combinations are oftenpreferred. For example, digital gain adjustment often has highresolution, is easy to implement and does not introduce I/Q mismatch. Onthe other hand, modifying the digital gain may increase the dynamicrange requirements of the analog elements of chain 150. For a chainhaving a limited analog dynamic range, the gain adjustments aretypically split between the analog and the digital domains.

FIG. 5 is a block diagram that schematically illustrates an alternativetransmitter chain configuration 176, in accordance with an alternativeembodiment that is described herein. The example of FIG. 5 refers to adual-carrier transmitter. Most of the transmitter chain elements areduplicated per each uplink carrier, but the two carriers are amplifiedby a single PA 174. The outputs of mixers 170 are summed by a powercombiner 178, whose output is provided to PA 174. Each transmitter chainhas a separate setting of analog and digital gain, all set by PC unit138. This configuration may be suitable, for example, when the twocarriers are closely spaced in frequency.

In many practical cases, the PA has a certain power constraint whenjointly transmitting the two carriers. For example, the maximum power ofthe signal at the PA input may not be allowed to exceed a certain level,so as to limit the level of non-linear distortion at the PA output. Insome embodiments, the PC unit takes this constraint into considerationwhen setting the power levels of the two carriers.

FIG. 6 is a block diagram that schematically illustrates yet anothertransmitter chain configuration 180, in accordance with an alternativeembodiment that is described herein. In the example of FIG. 6, thedigital elements of the transmitter chain are duplicated for eachcarrier, but the analog stages are common to the two carriers. Theoutputs of digital gain stages 158 are combined digitally using acombiner 184, and the composite digital signal is provided to D/Aconverter 162. In the present example, the configurable analog gainstage is common to the two carriers. The digital gain setting isseparate for each carrier, but the analog gain is set jointly for thetwo carriers.

In the configuration of FIG. 6, PC unit 138 adjusts three parameters(two digital gains and one analog gain) in order to reach two desiredpower levels of the two carriers. For example, the PC unit may first setthe power level of the carrier having the higher power using the commonanalog gain and the digital gain of its respective transmitter chain.Then, the power level of the second carrier can be set using only thedigital gain of the second transmitter chain.

The transmitter chain configurations illustrated in FIGS. 4-6 are shownby way of example. In alternative embodiments, any other suitableconfiguration can also be used. For example, additionally oralternatively to sharing common analog gain stages, the transmitterchains may share common digital gain stages, as well.

Although the embodiments described herein mainly address spectrumaggregation in E-UTRA (LTE and LTE-A) systems, the principles of thepresent disclosure can also be used in various other types ofcommunication systems, such as in various Universal MobileTelecommunications System (UMTS) networks, CDMA systems such asCDMA2000, WiMAX systems, Flash OFDM (as defined in IEEE 802.20specifications), WiFi systems (as defined in IEEE 802.11specifications), Global System for Mobile communications General PacketRadio Service (GSM/GPRS) systems and EDGE systems.

It will thus be appreciated from the foregoing that the embodimentsdescribed above are cited by way of example only, and that the presentdisclosure is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present disclosureincludes both combinations and sub-combinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofwhich would occur to persons skilled in the art upon reading theforegoing description and which are not disclosed in the prior art.

1. (canceled)
 2. A method for communication, comprising: in a wirelesscommunication terminal, modulating data to produce a composite,aggregated-spectrum signal comprising at least first and secondcomponent carriers, each component carrier configured to carry arespective portion of the modulated data, in respective first and secondspectral bands; transmitting the signal from the wireless communicationterminal to a base station, such that the first and second componentcarriers in the signal are transmitted at respective first and secondpower levels that are controlled individually; while communicating withthe base station, receiving at the wireless communication terminal oneor more instructions from the base station to set at least the firstpower level; and setting at least the first power level based on theinstructions, so as to modify a ratio between the first power level fortransmitting the first component carrier and the second power level fortransmitting the second component carrier.
 3. The method according toclaim 2, comprising receiving at the wireless communication terminal oneor more additional instructions to set the second power level, andsetting the second power level based on the additional instructions. 4.The method according to claim 2, wherein the component carriers comprisea plurality of the component carriers that are divided into two or moresubsets, wherein receiving the instructions comprises receiving a singlerespective power level setting for the component carriers comprised ineach of the subsets.
 5. The method according to claim 2, whereintransmitting the signal comprises transmitting the first and secondcomponent carriers such that the respective first and second spectralbands are non-contiguous.
 6. The method according to claim 2, whereinreceiving the instructions comprises receiving incremental correctionsto be applied to the first power level, wherein setting the first powerlevel comprises adjusting the first power level responsively to theincremental corrections.
 7. The method according to claim 2, whereinsetting the first power level comprises measuring signals received fromthe base station and calculating the first power level responsively tothe measured signals, wherein receiving the instructions comprisesreceiving correction factors to be applied to the calculated first powerlevel.
 8. The method according to claim 2, wherein transmitting thesignal comprises amplifying the first and second component carriersusing respective first and second transmitter chains, each of thetransmitter chains having a configurable digital gain stage and aconfigurable analog gain stage, comprising setting the first and secondpower levels by configuring the digital gain stage and the analog gainstage in at least one of the transmitter chains.
 9. The method accordingto claim 8, wherein at least two of the transmitter chains share acommon configurable analog gain stage.
 10. The method according to claim2, wherein each of the component carriers conforms to an EvolvedUniversal Terrestrial Radio Access (E-UTRA) specification. 11.Apparatus, comprising: a transmitter, which is configured to modulatedata so as to produce a composite, aggregated-spectrum signal comprisingat least first and second component carriers, each component carrierconfigured to carry a respective portion of the modulated data, inrespective first and second spectral bands, and to transmit the signalto a base station, such that the first and second component carriers inthe signal are transmitted at respective first and second power levelsthat are controlled individually; a receiver, which is configured toreceive, while communicating with the base station, one or moreinstructions from the base station to set at least the first powerlevel; and a processor, which is configured to control the transmitterto set at least the first power level based on the instructions, so asto modify a ratio between the first power level for transmitting thefirst component carrier and the second power level for transmitting thesecond component carrier.
 12. The apparatus according to claim 11,wherein the receiver is further configured to receive one or moreadditional instructions to set the second power level, wherein theprocessor is configured to set the second power level based on theadditional instructions.
 13. The apparatus according to claim 11,wherein the receiver is configured to receive a plurality of thecomponent carriers that are divided into two or more subsets, and toreceive a single respective power level setting for the componentcarriers comprised in each of the subsets.
 14. The apparatus accordingto claim 11, wherein the transmitter is configured to transmit the firstand second component carriers such that the respective first and secondspectral bands are non-contiguous.
 15. The apparatus according to claim11, wherein the receiver is configured to receive incrementalcorrections to be applied to the first power level, wherein theprocessor is configured to adjust the first power level responsively tothe incremental corrections.
 16. The apparatus according to claim 11,wherein the receiver and the processor are configured to measure signalsreceived from the base station and to calculate the first power levelresponsively to the measured signals, wherein the receiver is configuredto receive correction factors to be applied to the calculated firstpower level.
 17. The apparatus according to claim 11, wherein thetransmitter comprises first and second transmitter chains for amplifyingthe respective first and second component carriers, each of thetransmitter chains having a configurable digital gain stage and aconfigurable analog gain stage, wherein the processor is configured toset the first and second power levels by configuring the digital gainstage and the analog gain stage in at least one of the transmitterchains.
 18. The apparatus according to claim 17, wherein at least two ofthe transmitter chains share a common configurable analog gain stage.19. The apparatus according to claim 11, wherein each of the componentcarriers conforms to an Evolved Universal Terrestrial Radio Access(E-UTRA) specification.
 20. A mobile communication terminal comprisingthe apparatus of claim 11.